Modern integrated circuits generally contain several layers of interconnect structures fabricated above a substrate. The substrate may have active devices and/or conductors that are connected by the interconnect structure.
Interconnect structures, typically comprising trenches and vias, are usually fabricated in, or on, an interlayer dielectric (ILD). It is generally accepted that, the dielectric material in each ILD should have a low dielectric constant (k) to obtain low capacitance between conductors. Decreasing this capacitance between conductors, by using a low dielectric constant (k), results in several advantages. For instance, it provides reduced RC delay, reduced power dissipation, and reduced cross-talk between interconnects. Increased capacitance and resistance introduces a time delay that limits the maximum rate at which data can be transferred to and from the devices within an integrated circuit.
Examples of low k dielectric materials currently used include silicon dioxide and carbon doped oxide (CDO) materials. However, a low k material, such as silicon dioxide, typically has a dielectric constant in the range of 4. As the speed of integrated circuits continue to increase, lower k dielectric materials are needed to ensure time delays do not limit the faster rates at which data is transferred between devices at. One possibility for decreasing the dielectric constant of silicon dioxide and carbon doped oxide ILDs is to increase their porosity.
Yet, silicon dioxide at a dielectric constant of 4 exhibits a mechanical strength in the range of 80-100 GPa, while CDOs exhibits a mechanical strength in the range of 2-4 GPa. Increasing the porosity of these ILDs and lowering their mechanical strength may lead to mechanical and structural problems during subsequent wafer processing, such as during assembly and packaging. It is well known that diamond films exhibit very high mechanical strength, e.g. 1000 GPa. However, the dielectric constant of diamond films as deposited by such processes as chemical vapor deposition are typically about 5.7.
Additionally, current interconnect structures usually use copper, copper alloy, or some other metal as conductors to transfer data between devices. Using copper as a conductor in an interconnect structure potentially creates two problems: (1) dispersion of electrons and (2) electromigration of metal atoms. Dispersion of electrons occurs when electrons scatter in the lattice structure of a conductor degrading the signal sent across a conductor, such as copper. Electromigration occurs when metal atoms flow along with electrons across a conductor leaving holes. As interconnects become smaller, current densities increase, and the need for interconnect materials with good resistivity to electromigration and electron dispersion becomes more important.